Design and development of ferroelectric phase shifter for monolithic integration on silicon substrates

Development of ferroelectric thin film phase shifters on silicon for monolithic integration is the focus of this thesis. A general approach was initiated from the development of a BST thin film process on silicon substrate by RF reactive sputtering method. The effects of process parameters on the BST crystalline structure have been investigated to find optimum ranges for temperature, pressure, and surface conditions. Based on the analysis of crystalline property in BST thin films, highly crystalline BST thin films on SiO ₂/polysilicon was obtained without complex epitaxial buffer layers and a 50% dielectric tunability was demonstrated with a bias electric field of 250 KV/cm in a BI-CPW phase shifter.; In order to suppress inherent issues on silicon, polysilicon and SiO ₂ thin films are implemented. In addition, parallel plate type biasing has been introduced to reduce operating voltage and eliminate a bias-Tee and DC blocks from phase shifter device layout. Along with a periodic shunt circuit model, a new analytic formula with the approximation of CPW open-end line extension has been employed to obtain precise capacitance values from interdigital capacitors. The new approach has shown better accuracy than previous methods, due to the improved accuracy around finger end section.; By applying bilateral interdigital varactor with BST thin film, a compact phase shifter with the figure of merit of 27°/dB has been realized on an 8 mm2 area. The performance at 25 GHz in the newly developed phase shifter is competitive with other ferroelectric phase shifters on insulating ceramic substrates. The phase shifter has been fabricated by processes fully compatible with current MOS (metal oxide semiconductor) technology on high resistivity silicon, thus enabling the integration of phase controller in a chip. The great advantages of silicon use for monolithic integration, low production cost and the small device size provide critical benefits for commercial applications of phased array antennas in future wireless communication networks.